b) When the ball hits the ground, it is 0 ft above the ground. Find t when h 0. h 16t2 16t 20 0 16t2 16t 20 Substitute 0 for h. 0 4t2 4t 5 Divide by 4. t (4) 2(4)2 4(4)(–5) 2(4) Substitute a 4, b 4, and c 5. 4 116 80 8 Perform the operations. 4 196 8 4 416 8 196 116 16 416 4(1 16) 8 Factor out 4 in the numerator. t 1 16 2 Divide numerator and denominator by 4 to simplify. t 1 16 2 or t 1 16 2 The equation has two irrational solutions. t 1 2.4 2 or t 1 2.4 2 16 2.4 t 3.4 2 1.7 or t 0.7 Because t represents time, t cannot equal 1 16 2 . We reject this as a solution. Therefore, t 1 16 2 sec or t 1.7 sec. The ball will hit the ground after about 1.7 sec. Think carefully about the problem you are asked to solve. What does it mean in terms of the formula? YOU TRY 4 An object is thrown upward from a height of 12 ft. The height h of the object (in feet) t sec after the object is thrown is given by h 16t2 56t 12 a) How long does it take the object to reach a height of 36 ft? b) How long does it take the object to hit the ground? ANSWERS TO YOU TRY EXERCISES 1) a) {6, 3} b) e1 141 10 , 1 141 10 f 2) a) e 1 2 15 2 i, 1 2 15 2 i f b) {2 16, 2 16} 3) a) 39; two nonreal, complex solutions b) 121; two rational solutions c) 28; two irrational solutions d) 0; one rational solution 4) a) It takes 1 2 sec to reach 36 ft on its way up and 3 sec to reach 36 ft on its way down. b) 7 161 4 sec or approximately 3.7 sec 630 CHAPTER 10 Quadratic Equations and Functions www.mhhe.com/messersmith
messersmith_power_intermediate_algebra_1e_ch4_7_10
To see the actual publication please follow the link above